The implementation of novel electrophysiological interfaces to the brain, spinal cord, peripheral nerves, and muscles holds great promise for research into nervous-system function and for the future development of prosthetic devices. The goal of this project is the development and commercialization of an integrated platform for in vivo interfacing at the surface of neural tissue and muscle using conformable microelectrode arrays (MEAs). These MEAs are microfabricated using a technology that implements multilayer wiring and electrodes on a compliant polydimethylsiloxane (PDMS) substrate, and that creates a raised well around each electrode to facilitate tight coupling to the tissue. Electronics are integrated using a novel via bonding packaging technology that implements a robust, high-density electrical connection to the soft MEA substrate. The custom electronics facilitate the simultaneous stimulation and recording of the tissue in order both to control and to measure electrical activity. The Phase I SBIR project has two research and development aims with the following subaims: (1A) fabricate and test the compliant, raised-well MEAs, (1B) integrate the MEAs with proprietary electronics using the via bonding technology, (2A) validate the system performance by stimulating and recording from muscle, and (2B) validate the biocompatibility of the device for chronic implantation. Aim 1 will create the integrated platform and test the capability and robustness of the technology for future commercialization. Aim 2 will provide novel research data that will exemplify the power of the platform as a tool for the study of neuromuscular function. The successful completion of these aims will demonstrate both the applicability and the future potential of the technology. This project will provide a powerful tool that, by interfacing at the tissue surface, bridges the gap between highly invasive penetrating electrode arrays and low-fidelity cutaneous interfaces. The platform will facilitate research into a broad range of neurological and neuromuscular disorders and will have the potential to enhance the advanced development of prostheses and brain-machine interfaces to address the treatment of these disorders. The range of research and clinical applications includes the study of motor control and neuromuscular diseases and disorders, the implementation of prostheses to address conditions as far ranging as spinal-cord injury and blindness, and the development of brain-machine interfaces for the diagnosis and subsequent treatment of epilepsy.